Conventional container coatings may be derived from a thermally curable formulation that includes particles of a thermoplastic material in an organic solvent. Vinyl chloride polymers such as poly(vinyl chloride) (“PVC”) have frequently been employed as the thermoplastic material in such coatings. When these coatings are applied to a substrate and cured, the thermoplastic material can degrade and discolor. Degradation products such as, for example, hydrochloric acid (“HCl”) can attack the substrate.
To stabilize thermoplastic materials such as PVC and reduce degradation, epoxy resins may be added to the coating formulation. These epoxy resins typically include polyglycidyl ethers of aromatic polyols such as bisphenol A (often referred to as “BADGE”). Epoxy novolacs and epoxidized linseed oil have also been used as stabilizers for coating formulations containing thermoplastic materials such as PVC.
There is a desire to reduce or eliminate epoxy compounds from certain types of food-contact coatings. However, it has been problematic to formulate thermoplastic coating formulations that exhibit very low or non-detectable levels of mobile forms of these compounds while still retaining the required coating characteristics (e.g., flexibility, adhesion, corrosion resistance, stability, etc.).
Thus, there is a continuing need for improved coating compositions.